[llvm] GlobalISel: Use G_UADDE when narrowing G_UMULH (PR #97194)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> "We should have a combine to form G_UADDE from this pattern,". This will be answered in the Combiner.rst file. Are we allowed to write abstraction raising combines?

What do you mean by `abstraction raising` here? 

> In this case, I am strongly opposed. I don't want the combiner to create more legalization artefacts.

I don't follow. No legalization artifacts are mentioned here. It's an instruction, typically used for legalization, which should have a rich set of optimization combines on it. It is not a legalization artifact, nor are legalization artifacts something to be avoided 



https://github.com/llvm/llvm-project/pull/97194